Flexible or portable closure – partition – or panel – Plural strip – slat – or panel type – With mounting or supporting means
Reexamination Certificate
2000-04-12
2002-06-11
Lev, Bruce A. (Department: 3634)
Flexible or portable closure, partition, or panel
Plural strip, slat, or panel type
With mounting or supporting means
C160S189000, C160S193000, C160S201000, C049S200000
Reexamination Certificate
active
06401793
ABSTRACT:
BACKGROUND
The present invention relates generally to the field of sectional doors and related safety devices. More particularly, the present invention relates to novel hardware devices designed to improve safety and minimize the risk involved in installing, maintaining and operating sectional doors which utilize spring mechanisms to facilitate door movement.
Large doorways in garages, shops, stores, warehouses and other buildings often use sectional doors to enclose the doorway opening. These doors are generally constructed of wood or metal panels which are joined by metal hinges and hung from metal rollers which travel along a fixed track at each side of the door. Sectional doors typically range in size from small storage unit models of just a few feet wide to very large models which accommodate trucks and heavy equipment. Sectional doors are used for residential garages where they are found in one and two car sizes.
The size of sectional doors and the weight of their materials make them relatively heavy and, therefore, difficult to lift. Many doors also contain insulation and other materials which further add to the door's weight. Even an average-sized residential garage door can weigh several hundred pounds, making it impossible for the average person to lift.
As a consequence of the weight of sectional doors, mechanisms have been invented to counteract the door's weight thereby allowing manual operation of the door. One common method of counteracting a door's weight is accomplished with a counterspring mechanism using springs which are displaced elastically as the door is shut, thereby exerting a lifting force on the door as it is closed. This spring force slows the fall of the door during closing and aids significantly in lifting the door; in effect, the door weight is balanced.
Coil springs, in a torsion spring configuration, are often used for these mechanisms. In a torsion spring configuration, the coil spring is deflected or wound around the axis of its helix. In a typical coil spring configuration, as shown in
FIG. 1
, one or more coil springs
2
are wound around a shaft
4
near the top of the door
6
. One end of each coil spring
2
is attached to a mounting bracket
8
which is connected by screws
12
to the building structure which is typically a wooden beam
14
across the door opening. The other end of the spring is attached to a cable drum pulley
16
around which a cable
18
is wound. The cable
18
extends to the bottom of the door where it is attached with a bracket
20
. These coil springs are pre-wound or pre-tensioned to increase lifting potential and ensure that the door is lifted to a fully opened position.
As the door closes, the cable unwinds from the cable drum pulley thereby twisting the spring and increasing the torsion on the spring and the energy stored within the spring. A properly adjusted spring mechanism will exert a force on a door that is about the same as the weight of the door allowing a user to open the door with the slightest of lifting effort. This means that the ideal spring mechanism, on an average door, will need to store an amount of energy that is approximately equal to the weight of the door. In terms of force and considering the lever arm of the cable drum, the spring holds a force of at least twice the weight of the door. Consequently, these spring mechanisms store a great deal of energy that is unleashed as a twisting force. Under proper operating conditions, this mechanism results in a smoothly operating door, but when poorly or improperly maintained or installed this force can be instantly unleashed in an injurious and even deadly fury.
One problem area where serious injuries can occur is at the location where the spring mounting bracket
8
attaches to the building. The spring mounting bracket is usually attached to a wood header or beam spanning across the doorway opening or vertical wood stud members.
These beams, headers or studs are typically wood members that sometimes have a relatively high moisture content at the time of construction. Over time the wood loses its natural moisture, causing shrinkage, warping or bowing of the framing members as the shrinkage pattern encounters natural inconsistencies in the grain of the wood. Cracking also results from this natural moisture loss leaving large voids in what was once solid lumber. As a result of this drying process, holes drilled for screws and mounting hardware may expand, crack and otherwise deform leaving the screws or other connectors loose and structurally weakened.
The connection to the wood support is typically made with lag screws which penetrate holes in the bracket and thread into drilled holes in the wood. This type of connection generally appears structurally sound over the short term, but problems may arise with wood shrinkage and installation problems. As the wood shrinks, the screw holes expand and the grip on the screw threads decreases and fails. Problems may also arise from installation error or misjudgment. Holes for lag screws should be drilled to an exact size to provide optimal screw capacity. When holes are over-bored to a diameter that is larger than the optimal size for the screw, the screw's holding capacity is greatly diminished. Similarly, a hole may be drilled too small or not at all which may cause the wood to crack when the lag screw is installed or a screw is inserted. Likewise, a lag screw or other fastener may be over-tightened, causing the screw thread to twist within the hole, thereby removing some of the wood material within the hole and effectively stripping the hole interior. This also weakens the screw's holding capacity.
Often, siding material is applied to the interior face of the doorway structure to which the spring mounting bracket is attached. Generally, this siding is a gypsum-based “drywall” or “sheetrock” material that provides fire-proofing and aesthetic benefits but has very little structural strength. Screws and other fasteners which must penetrate this layer have considerably lower holding capacity due to the decreased fastener penetration into the sound structural wood below. Sometimes a piece of 2×4 or 2×6 is nailed through the sheetrock to the structure below, to which the spring mounting brackets are fastened. In this situation, the spring's torsional force is now contained only by the nails.
The problem is exacerbated by the repetitive vibration the connection must endure. The vibration and stress caused by the repeated opening and closing of the door, especially when performed by high-speed electric openers, can be an additional and significant factor in connection failure. Screw connections that are already weakened by the above-mentioned factors can vibrate loose and screws can even wiggle right out of their holes.
When the mounting bracket connection fails, the entirety of the stored torsional energy of the door spring is instantaneously unleashed, typically through uncontrolled, high-velocity spinning of the sharp-edged metal mounting bracket. When this failure occurs, any person or thing in close proximity to the bracket will be injured or destroyed. The energy of the spring mechanism is sufficient to cause severe injury and can easily maim, dismember or kill a person who is near the unit at the time of failure.
A dangerous situation often presents itself when an unwary homeowner or repairman observes loose or missing fasteners on the spring mounting bracket. Generally, the observer's reaction is to tighten the loose fasteners. This typically requires the “repairman” to climb a ladder, putting himself in very close proximity to the spring mounting bracket while tightening the loose fastener with a wrench. If the holes have expanded due to drying or have been stripped out or otherwise weakened, the attempted “tightening” will generally cause further weakening of the connection which is under spring force load often causing complete connector failure. When complete connector failure occurs, the spring force is instantly released by the wildly spinning moun
Broadbent Berne S.
Kirton & McConkie
Lev Bruce A.
Martin Door Manufacturing, Inc.
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